The invention relates to a switching configuration for a telephone system, such as a PBX, with subscriber line and trunk groups, in which the respective groups and the combined subscriber line/trunk groups are each connected via a common interface module for each such group, both to the speech path switching network, and via a data transmission trunk group, to a central controller. The central controller is provided to establish the switching paths of incoming and outgoing subscriber lines and trunks. Information is transmitted via the speech path switching network using pulse code modulation and the information is transmitted via the data transmission trunk group using a message format with variable data length (HDLC procedure). In addition, an interface circuit is assigned to each interface module for the purpose of transmitting to or receiving from the subscriber lines and/or the trunks, and for buffering voice signal data, and for status monitoring.
In "Telcom Report 2" (1979), Vol. 3, pages 174-83, the architecture of a new line of digital public switching systems is disclosed. In these systems subscriber lines and trunk groups are connected to a speech path switching network via a respective common interface for each such group. The speech information is transmitted via the speech path switching network using pulse code modulation. The remaining information required for establishing the switching paths, which is to be transmitted to a group processor assigned to the group, is directly applied to this group processor via separate data transmission trunks. The other information required for establishing the switching paths and for processing in the central controller is exchanged between the interface modules and the central controller, or between the group processors and the central controller, via separate data trunks, and via a group switch and the common switching network. The speech information transmitted via the speech path switching network is transmitted using pulse code modulation. The information supplied via the individual data transmission trunk groups or the common signaling channels is transmitted using a message format with variable data length (HDLC procedure).
In "NEC Research and Development", No. 64, January 1982, pages 86-93 an NEAX 61 digital transmission system is disclosed. In this system information is exchanged between central controllers (RLOC and HDTIC) via individual transmission paths which also include, in part, speech transmission paths. The speech information is transmitted using pulse code modulation. The information to be transmitted between the central controllers is converted from the message format with a variable data length into pulse code information. It is then transmitted via the transmission path mentioned above in a specific pulse frame of a specific length.
However, the previously mentioned exchange of information between the central controllers does not take place via the interface modules, which operate on an analog basis in this system.